Today the use of fiberoptic bronchoscopy is a common and standard diagnostic procedure, which allows direct observation of the upper and lower conducting airways. During passage of the endoscope through the nasopharynx, trachea, and large bronchi, the quantity of mucous secretions can be assessed readily in addition to the degree of mucosal edema and bronchospasm. In addition to examination of the airway lumen, one of the greatest advantages and rewards from bronchoscopy is the ability to sample the large and small airways and the alveoli. The specimens collected are then analyzed for their cellular and noncellular constituents.
In recent years, bronchoalveolar lavage (bronchoalveolar lavage) using either an endoscope or specialized tubing has gained some popularity over more traditional sampling methods such as tracheal aspiration for most cases in which a diffuse inflammatory disorder is suspected. For many years, it has been assumed that sampling the lower trachea provides a representative impression of the alveoli and small airways because airway free cells from the peripheral lung eventually were swept toward the trachea for clearance.
However, a large clinical case survey of young athletic horses presented with poor performance attributable to the lower respiratory system has shown that the cytologic and bacteriologic results are correlated poorly between samples obtained from the tracheal aspirate versus those from bronchoalveolar lavage. The study demonstrated that tracheal aspirate and bronchoalveolar lavage cytologic cell differential counts differed greatly within the same horse, which suggests that samples from the tracheal puddle may not reflect accurately the population of cells and secretions present within the small airways and alveoli. This is relevant insofar as exercise intolerance, airway injury resulting from inflammation, and airway hyperreactivity are associated with disease in the small airways, reflected best by bronchoalveolar lavage cytology. In addition, a higher rate of positive bacterial cultures was obtained from tracheal aspirate samples versus bronchoalveolar lavage samples performed on the same occasion. Thus the lower trachea apparently harbors a normal bacterial flora that may not be present within the small airways and alveoli. For these reasons, bronchoalveolar lavage is becoming a more popular tool to assess distal (small) airway inflammation rather than the tracheal aspirate method of sampling.
To validate the relevance of bronchoalveolar lavage differential cell counts as a complementary diagnostic tool in the assessment of the respiratory system, other quantitative measurements are necessary beyond the routine clinical examination. In the last two decades, the syndrome of heaves has been studied extensively, and several research laboratories throughout the world have clearly demonstrated a high correlation between the bronchoalveolar lavage cell differential and results of pulmonary function testing and histamine bronchoprovocation in heaves-affected horses. In recent years, similarly characterized lung function in young athletic horses with noninfectious inflammatory airway disease (IAD) has paralleled these findings with respect to the diagnostic usefulness of bronchoalveolar lavage.
The purpose of this chapter is to discuss the use of the bronchoalveolar lavage technique as a tool to identify and characterize pulmonary inflammation in horses that suffer from diffuse lung pathology such as inflammatory airway disease in the young athletic horse and the heaves syndrome in mature horses. In addition viral and bacterial pulmonary conditions are discussed briefly with respect to their diagnosis by bronchoalveolar lavage.
Bronchoalveolar Lavage Procedure
bronchoalveolar lavage can be performed on most conscious horses with mild sedation (xylazine 0.3-0.5 mg/kg IV or romifidine 0.03-0.05 mg/kg IV) and airway desensitization by a local anesthetic (lidocaine solution 0.4% w/v, without epinephrine). The procedure can be conducted using either a bronchoscope 1.8 to 2 m in length or a specialized bronchoalveolar lavage tube (Bivona Medical Technologies, Gary, Ind.). Once the bronchoscope or bronchoalveolar lavage tube is in the trachea, reaching the tracheal bifurcation (carina) usually induces coughing. Infusing 60 to 100 ml of prewarmed lidocaine solution (0.4%, without epinephrine) is therefore beneficial at this point to desensitize cough receptors located at the carina. After this infusion step the endoscope or bronchoalveolar lavage tube is gently but securely wedged, as detected by resistance to further advancement. Prewarmed sterile saline (200-300 ml) is infused rapidly into the lung and is subsequently aspirated.
The total amount of saline should be divided into two separate boluses for infusion, with attempts to retrieve as much fluid as possible between each bolus. In general, retrieval of 40% to 60% of the total amount of infusate indicates a satisfactory bronchoalveolar lavage. In horses with advanced disease, lower volumes are recovered and a tendency exists for less foam (surfactant) to be present. The bronchoalveolar lavage fluid samples are then pooled and kept on ice if processing is not possible within 1 hour after collection. Gross examination of the fluid should be performed to detect any flocculent debris or discoloration. One or two serum or ethylenediaminetetraacetic acid (EDTA) tubes of bronchoalveolar lavage fluid are centrifuged (1500 X g for 10 min) and air-dried smears are made from the sample pellet after removal of the supernatant. In preparation of the smears, the slides must be air dried rapidly using a small bench-top fan to preserve good cellular morphology. Smears thus prepared can be kept at room temperature for up to 8 to 10 months with little cellular alterations. The air-dried smears can be stained with Diff-Quik, Wright-Giemsa, May Gruenwald, Leishman’s, or Gram’s stain for cellular and noncellular constituent interpretation. The cellular profile and morphology may serve as a guide to the nature of airway injury, inflammation, and the pulmonary immunologic response to infections or foreign antigens.
bronchoalveolar lavage is undoubtedly becoming a powerful ancillary diagnostic tool to assist in the diagnosis of clinical and sub-clinical lower airway respiratory conditions such as non-infectious inflammatory airway disease in the young athletic horse and recurrent airway obstruction, or heaves, in older horses. Using recognized, standardized procedures, the bronchoalveolar lavage differential cell count is fairly consistent for normal horses and any alteration in the cytologic profiles from normal values identifies a wide range of nonseptic inflammatory processes. Although at present, clinicians are recommending specific treatment according to cytologic findings of the bronchoalveolar lavage cell differential, a more in-depth knowledge of the various disorders in the future may allow equine practitioners to provide more accurate prognostic information to members of the horse industry with respect to respiratory diseases in athletic horses. More so, the majority of young and mature athletic horses with an excess amount of white mucopus within the airways and markedly elevated neutrophil percentage on the cell differential do not represent a septic process. Rather, these cases demonstrate nonseptic inflammatory airway disease.